Title:  IGS Ultra rapid products for (near-) real-time applications
Author: T.A. Springer

Abstract.

Since GPS week 1052, 5 March 2000, the IGS is producing a new combined
orbit product. This product is called the IGS Ultra rapid orbit, IGU.
The combined IGS Ultra rapid orbits are being made available twice every
day, at 03:00 and 15:00 UTC, with a delay of 3 hours and are based on
solutions from up to 7 different IGS Analysis Centers.

Each ultra rapid orbit file covers 48 hours. The first 24 hours of the orbit
are based on actual GPS observations (real orbit) the second 24 hours are
extrapolated (predicted orbit). Like the IGS Predicted (IGP) orbits the Ultra
rapid orbits are available for real-time usage. However, the quality of the
Ultra rapid orbits should be significantly better because the average age of
the predictions is reduced from 36 hours (IGP) to 9 hours (IGU). When the
quality of the IGU products reaches a satisfactory level the IGU products
will replace the IGP products. The main reason for the generation of the
Ultra rapid products are the requirements, in both timeliness and accuracy,
for near-real-time atmospheric monitoring, e.g., weather predictions.

In this presentation we will show first results of the IGS Ultra rapid
combinations. By comparing the IGU product to the other IGS products
we will demonstrate the quality of this new product. In particular we will
compare its quality to the IGP (predicted) product. Besides these comparisons
we will also use the different IGS products to process a small GPS network and
compare the results. The focus will be on the differences in the tropospheric
zenith delay estimates because these are the parameters which are the
"driving force" behind the IGS Ultra rapid products.